1. Technical Field
This invention relates to the field of cell-based assays. In particular, the invention provides impedance-based devices, apparatuses and systems for analyzing cells and for conducting cell-based assays.
2. Background Art
A. Electronic Analysis of Cells
Bioelectronics is a progressing interdisciplinary research field that involves the integration of biomatereials with electronic devices. Bioelectronic methods have been used for analyzing cells and assaying biological molecules and cells. In one type of application, cells are cultured on microelectrodes and cell-electrode impedance is measured and determined to monitor cellular changes.
In PCT Application No. PCT/US03/22557,entitled “IMPEDANCE BASED DEVICES AND METHODS FOR USE IN ASSAYS”, filed on Jul. 18, 2003, a device for detecting cells and/or molecules on an electrode surface is disclosed. The device detects cells and/or molecules through measurement of impedance changes resulting from the attachment or binding of cells and/or molecules to the electrode surfaces. A number of embodiments of the device is disclosed, together with the apparatuses, system for using such devices to perform certain cell based assays.
B. Allergic Diseases and IgE-mediated Cell Activation
Allergic diseases, also commonly known as immediate hypersensitivity disorder are the most common dysfunction of the immune system afflicting 20% of all individuals in the United States. The immediate hypersensitivity response can range anywhere from a simple rash or itchy and watery eyes to the most extreme case of anaphylaxis, where the airways are restricted to the point of asphyxiation and death. Due to the severity of the hypersensitivity responses, the lack of adequate treatment and the high percentage of the population suffering from various forms of this condition, the pharmaceutical industry has taken a keen interest in developing novel drugs to effectively treat and combat the symptoms of this disabling and potentially life threatening disorder.
The primary cells of the immune system that are involved in the allergic response are mast cells, basophils and eisonophils. Basophils and eisonophils differentiate in the bone marrow, circulate in the blood and are recruited to the sites of the inflamed tissue in the late-phase of the reactions. In contrast, mast cells are normally distributed throughout the connective tissue and are the involved in the immediate phase of immunoglobulin E (IgE)-mediated allergic reactions (Sharma et al. Clin Rev Allergy Immunol. 2002 April;22(2):119–48). The initial encounter of an individual with an allergen leads to the production of IgE, which binds to the high affinity IgE receptor (Fc(epsilon)RI) on the surface of mast cells causing sensitization of the mast cells. Subsequent encounter with the allergen leads to cross-linking of the Fc(epsilon)RI-IgE complex on the surface of mast cells and stimulation of the mast cells to release mediators of immediate hypersensitivity. The cross-linking of receptor-bound IgE on the mast cell surface triggers a sequence of intracellular events, collectively referred to as mast cell activation that culminate in the extracellular release of potent inflammatory mediators, many of which are stored in the secretory granules, including histamine. Mast cell activation can be divided into an interdependent early and late phase. The early phase of mast cell activation include phosphorylation and activation of protein tyrosine kinases and their substrates, generation of the second messengers inositol-tris phosphate and diacylglycerol, elevation of intracellular calcium levels and fusion of secretory granules with the membrane (Stassen et al. Crit Rev Immunol. 2002;22(2):115–40). The late phase of mast cell activation includes dramatic morphological changes due to remodeling of the actin cytoskeleton, gene expression leading to the synthesis and secretion of potent inflammatory cytokines and synthesis of lipid mediators that have variety of effects on blood vessels, bronchial smooth muscle and leukocytes.
Based on the various steps involved in the initiation and execution of the immediate hypersensitivity response, there are multiple potential targets for pharmaceutical intervention. The bulk of the current therapies for immediate hypersensitivity disorders such as asthma seek to alleviate the symptoms of the condition rather than directly target the underlying cause. However, current promising efforts are underway to neutralize the IgE antibody by administration of humanized monoclonal anti-IgE antibody and to achieve long term alleviation of clinical symptoms (D'Amato et al. Monaldi Arch Chest Dis. 2003 January–March;59(1):25–9). Also, the elucidation of the intrinsic signaling pathways underlying IgE-mediated mast cell activation together with the advent of combinatorial chemistry provide ample opportunity to employ small molecular inhibitors to target key proteins and enzymes involved in mast cell activation. These compounds could potentially provide novel immunomodulators for the treatment of immediate hypersensitivity disorder. Small molecular inhibitors of several kinases, including PKC and the tyrosine kinase Syk have provided encouraging preclinical results in rodent studies in blocking some immediate hypersensitivity responses (Seow et al. Eur J Pharmacol. 2002 May 17; 443(1–3):189–96).
An increasing number of companies are utilizing large chemical libraries to screen for potential inhibitors of signaling pathways that maybe involved in various disease states. Hence, there is an urgent need for high-throughput molecular and cellular assays to screen for potential modulators of these signaling pathways. With regards to IgE-mediated signaling, the current assays measure mediators that are released into the media after degranulation. This is accomplished by either measuring the enzymatic activity of these mediators (Rac and phosphatidylinositol 3-kinase regulate the protein kinase B in Fc epsilon RI signaling in RBL 2H3 mast cells. J Immunol. 2001 Feb. 1;166(3):1627–34), using radioactive precursors (Guillermot et al. J Cell Sci. 1997 September; 110 (Pt 18):2215–25), or by ELISA, quantifying the amount of mediators that are released (Berger et al. Allergy. 2002 July;57(7):592–9). These assays are single point assays or endpoint assays which measure the cumulative release of these mediators and also involve utilization of reagents and manipulation of the cells, such as fixation or lysis. The fact that these are single point assays, which utilize expensive reagents such as antibodies and cellular manipulation, does not warrant adaptability for high-throughput analysis that is required to screen large chemical libraries.
C. Anticancer Drug Screening and Discovery
In anticancer drug development, the study of the time dependence of cytotoxic and cell proliferation inhibitory effect of a drug is an important element for gaining information to use in the development of clinical dosing strategies. In particular, time dependent IC50's are derived and different time dependent patterns for IC50's are observed (e.g., see Hassan S B, Jonsson E, Larsson R and Karlsson M O in J. Pharmacology and Experimental Therapeutics, 2001, Vol. 299, No. 3, pp 1140–1147; Levasseur L M, Slocum H K, Rustum Y M and Greco W R, in Cancer Research, 1998, vol. 58, pp 5749–5761.). Typically, these studies used end-point single-measurement assays. Each time point for a dose concentration of drug or compound applied to the cultured cells required a separate experiment. This limits the time resolution and the number of time points of such time-dependent cytotoxicity studies. Thus, new technologies or methods that can provide higher time resolution and permit measurements on many time points are needed.
The present invention further expands the inventions disclosed in PCT Application No. PCT/US03/22557, entitled “IMPEDANCE BASED DEVICES AND METHODS FOR USE IN ASSAYS”, filed on Jul. 18, 2003 and disclosed in U.S. patent application Ser. No. 10/705,447, entitled “IMPEDANCE BASED DEVICES AND METHODS FOR USE IN ASSAYS,” filed on Nov. 10, 2003. The invention provides a real time cell electronic sensing system for conducting cell-based assays based on measurement of cell-substrate impedance and provides the method for using such a system to perform cell-based assays. Furthermore, the present invention is aimed at addressing the limitations in current methods and technologies for assaying IgE-mediated signaling and cell activation.